JP4242079B2 - Positive electrode active material for lithium secondary battery and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material for a lithium secondary battery and a method for producing the same, and more particularly to a method for producing a positive electrode active material for a lithium secondary battery capable of producing a positive electrode active material exhibiting excellent life characteristics by a simple process. .
[0002]
[Prior art]
A lithium secondary battery is manufactured by using a material capable of reversibly inserting and removing lithium ions as a positive electrode and a negative electrode, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode. Electric energy is generated by oxidation and reduction reactions when inserted / desorbed at the positive and negative electrodes.
[0003]
Lithium metal has been used as the negative electrode active material for lithium secondary batteries, but when lithium metal is used, there is a risk of explosion due to battery short circuit due to the formation of dendrites. It has been replaced by carbonaceous materials such as carbon or crystalline carbon.
[0004]
As the positive electrode active material is a chalcogenide (chalcogenide) compound is used, examples thereof _{LiCoO 2, LiMn 2 O 4,} LiNiO 2, LiNi 1 - x Co x O 2 (0 <x <1), such as LiMnO ₂ Composite metal oxides have been studied. Mn-based positive electrode active materials such as LiMn ₂ O ₄ and LiMnO _{2 in the} positive electrode active material are easy to synthesize, are relatively inexpensive, and are less attractive to the environment. Has disadvantages. In addition, LiNiO ₂ has the disadvantage that it is the cheapest among the positive electrode active materials described above, and shows the battery characteristics of the highest discharge capacity, but is difficult to synthesize. Furthermore, LiCoO ₂ is a typical positive electrode active material that is commercially available and commercially available from Sony, etc., although it exhibits good electrical conductivity, high battery voltage, and excellent electrode characteristics, but it is expensive. There is.
[0005]
Generally, the composite metal oxide is synthesized by solid reaction of a mixture of raw material oxides. The solid reaction is a method of producing a target compound by mixing a raw material powder in a solid state and then firing and ball milling several times. For example, Sony has heat-treated Li _x CoO ₂ active material using an oxide such as Co (OH) ₂ or Co ₃ O _{4 at} 800 to 900 ° C. for several tens of hours, followed by pulverization and particle size separation. Manufacture. In Matsushita, a two-stage continuous sintering process is used. In the first stage, LiOH, Ni oxide, and Co oxide are reacted at 400 to 580 ° C. to form an initial oxide, and the second stage. Then, a complete crystalline material is synthesized by heat treatment at 800 ° C. for several tens of hours. The LiMn ₂ O ₄ active material is also synthesized by the solid reaction described in detail using a metal oxide such as LiOH and MnO ₂ .
[0006]
[Problems to be solved by the invention]
However, the conventional method for producing a composite metal oxide has a disadvantage in that it requires a lot of equipment and time through complicated steps. In addition, the synthesis method using the existing composite metal oxide has a relatively high synthesis temperature, and the size of the reactant particles is relatively large, and the shape of the active material particles (Morphology) and surface characteristics (surface area, pore size) It is difficult to adjust physical properties such as
[0007]
The physical properties of the active material are important factors that greatly affect the electrochemical characteristics of the battery. In order to maximize the characteristics of the battery, it is necessary to be able to arbitrarily adjust the physical properties of these active materials. In other words, the characteristics of the battery are significantly affected by the physical properties of the composite metal oxide that is the synthesized active material, but the active material of the composite metal oxide synthesized at a high temperature by the solid state method is the initial starting material. It is very difficult to change the physical properties because it depends only on the properties of the material. Therefore, a method and research for changing the physical properties of the final composite metal oxide active material powder are actively progressing.
[0008]
In particular, LiCoO ₂ that exhibits good electrical conductivity, high battery voltage, and excellent electrode characteristics is heat-treated at a high temperature of about 800 to 900 ° C. for several tens of hours using an expensive oxide such as Co ₃ O _4. The problem is that the price is very high due to the synthesis.
[0009]
The present invention is for solving the above-mentioned problems, and an object of the present invention is to provide a method for producing a positive electrode active material for a lithium secondary battery, which can produce a positive electrode active material by a simple process. It is in.
[0010]
Another object of the present invention is to provide a method for producing a positive electrode active material for a lithium secondary battery capable of economically producing a positive electrode active material.
[0011]
Another object of the present invention is to provide a positive electrode active material for a lithium secondary battery that exhibits excellent life characteristics.
[0012]
[Means for Solving the Problems]
In order to achieve the object described in detail, the present invention provides a positive electrode active material for a lithium secondary battery by refluxing a lithium salt and a metal salt on an aqueous solution of KOH or NaOH or an organic solution of KOH or NaOH. Provide a method.
[0013]
The present invention also provides a positive electrode active material for a lithium secondary battery having a spherical or similar spherical shape, a particle size of 10 nm to 10 μm, and a surface area of 0.1 to 5 m ² / g. The positive electrode active material of the present invention is a compound selected from the following chemical formulas 1 to 14.
[Chemical formula 1]
Li _x MnA ₂
[Chemical formula 2]
Li _x MnO _2-z A _z
[Chemical formula 3]
Li _x Mn _1-y M´ _y A ₂
[Chemical formula 4]
_{Li x Mn 1-y M'y} O 2-z A z
[Chemical formula 5]
Li _x Mn ₂ O ₄
[Chemical formula 6]
Li _x Mn ₂ O _4-z A _z
[Chemical formula 7]
Li _x Mn _2-y M´ _y A ₄
[Chemical formula 8]
Li _x BA ₂
[Chemical formula 9]
Li _x BO _2-z A _z
[Chemical formula 10]
Li _x B _1-y M ^〃 _y A ₂
[Chemical formula 11]
Li _x Ni _1-y Co _y A ₂
[Chemical formula 12]
Li _x Ni _1-y Co _y O _2-z A _z
[Chemical formula 13]
Li _x Ni _1-yz Co _y M ^〃 _z A ₂
[Chemical formula 14]
Li _{x '} Ni _1-y' Mn _{y '} M´ _z' A _α
(In the above formula, 0.95 ≦ x ≦ 1.1, 0.01 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.5, 0.95 ≦ x ′ ≦ 1, 0.01 ≦ y ′ ≦ 0.5, 0.01 ≦ z ′ ≦ 0.1, 0.01 ≦ α ≦ 0.5, M ′ is made of Al, Cr, Mn, Fe, Mg, La, Ce, Sr and V A transition metal selected from the group or at least one metal of a lanthanoid metal, and ^M〃 is a transition metal selected from the group consisting of Al, Cr, Co, Mg, La, Ce, Sr and V, or (One or more of the lanthanide metals, A is selected from the group consisting of O, F, S and P, and B is Ni or Co.)
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
[0015]
The present invention is a positive electrode active material for a lithium secondary battery, which exhibits good electrical conductivity, high battery voltage and excellent electrode characteristics, but is a simple process for a cobalt-based positive electrode active material that is difficult to use due to its high price. The present invention relates to a production method that can be produced economically using
[0016]
The production method of the present invention can be applied not only to a cobalt-based positive electrode active material but also to a manganese-based, nickel-based, or nickel-cobalt-based positive electrode active material.
[0017]
Production method of the present invention, a lithium salt and a metal salt, an aqueous solution of KOH or NaOH, or KOH or NaOH was refluxed reacted on organic solution, refluxing the reaction was dried in Formula 1 through 14 below A compound is produced. That is, according to the present invention, a crystalline compound can be produced simply by a reflux reaction without the need for performing a heat treatment step.
[0018]
In general, the reflux method used in the present invention is a method in which a reactant is introduced into a reaction vessel, and then the temperature is increased to volatilize a volatile solvent from the reactant. A method of returning the part to the reaction vessel again. In other words, this method is a method for producing a compound by repeatedly generating and growing particles through an evaporation and condensation process in a solution state. This method is mainly used for the synthesis of organic compounds.
[0019]
In the present invention, the reflux reaction is carried out at 50 to 500 ° C., preferably 50 to 200 ° C. for 12 hours to 96 hours. If the reaction temperature is less than 50 ° C., there is a problem that the reaction does not proceed due to low reaction energy, and if it exceeds 500 ° C., there is a problem in manufacturing the reaction apparatus. In addition, when the reaction time is less than 12 hours, there is a problem that the reaction is not completed. It is sufficient to react for 96 hours, and it is not necessary to react further.
[0020]
Lithium nitrate, lithium acetate or lithium hydroxide can be used as the lithium salt, and manganese salt, cobalt salt, nickel salt or a mixture thereof can be used as the metal salt. As the manganese salt, manganese acetate or manganese dioxide can be used, as the cobalt salt, cobalt hydroxide, cobalt nitrate or cobalt carbonate, and as the nickel salt, nickel hydroxide, nickel nitrate or Nickel acetate can be used. Further, a fluoride salt such as manganese fluoride or lithium fluoride, or a sulfide salt such as manganese sulfide or lithium sulfide, or a phosfollows salt such as H ₃ PO ₄ may be further used. The lithium salt, manganese salt, cobalt salt, nickel salt, fluoride salt, sulfide salt or phosphorous salt is generally used for lithium secondary batteries, and the present invention is not limited to the above compound.
[0021]
As the solution, a basic aqueous solution prepared by dissolving a basic compound of KOH or NaOH in water , or an organic solution prepared by dissolving KOH or NaOH in an organic solvent can be used. As the organic solvent, alcohol such as methanol, ethanol or propanol, ether or acetone can be used, but the organic solvent is not limited thereto.
[0022]
The basic aqueous solution of KOH or NaOH preferably uses a base having a pH of 7 to 14, preferably a pH of 10 to 14. When the pH of the aqueous solution is less than 7, there is a problem that the reaction does not proceed.
[Chemical Formula 1] Li _x MnA ₂
[Chemical Formula 2] Li _x MnO _2-z A _z
[Chemical Formula 3] Li _x Mn _1-y M ′ _y A ₂
[Chemical Formula _{4] Li x Mn 1-y} M 'y O 2-z A z
[Chemical Formula 5] Li _x Mn ₂ O ₄
[Chemical Formula 6] Li _x Mn ₂ O _4-z A _z
[Chemical Formula 7] Li _x Mn _2-y M ′ _y A ₄
[Chemical Formula 8] Li _x BA ₂
[Chemical Formula 9] Li _x BO _2-z A _z
[Chemical Formula 10] Li _x B _1-y M ″ _y A ₂
[Chemical Formula 11] Li _x Ni _1-y Co _y A ₂
[Chemical Formula 12] Li _x Ni _1-y Co _y O _{2 -z} A _z
[Formula 13] Li _x Ni _1-yz Co _y M ″ _z A ₂
[Chemical Formula 14] Li _{x ′} Ni _{1-y ′} Mn _{y ′} M ′ _{z ′} A _α
(In the above formula, 0.95 ≦ x ≦ 1.1, 0.01 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.5, 0.95 ≦ x ′ ≦ 1, 0.01 ≦ y ′. ≦ 0.5, 0.01 ≦ z ′ ≦ 0.1, 0.01 ≦ α ≦ 0.5, and M ′ is made of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, and V. A transition metal selected from the group or at least one of lanthanoid metals, and M ″ is a transition metal selected from the group consisting of Al, Cr, Co, Mg, La, Ce, Sr and V, or (One or more of the lanthanide metals, A is selected from the group consisting of O, F, S and P, and B is Ni or Co.)
[0023]
Hereinafter, a manufacturing method of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, a volumetric flask (volumetric Flask) of the recirculation device lithium salt and a metal salt in a container 3 such as, and a basic aqueous solution of KOH or NaOH or add KOH or solution comprising an organic solution of NaOH,.
[0024]
Next, the temperature is increased to 50 to 500 ° C., preferably 50 to 200 ° C., measured with the thermometer 5 using the hot plate 1, and then refluxed while stirring at that temperature for 12 to 96 hours. Let At this time, a mixture of a lithium salt, a metal salt , and a basic aqueous solution of KOH or NaOH, or an organic solution of KOH or NaOH, and continuously passing through a reflux process, the seeds of Formulas 1 to 14 are passed through a seed. A crystalline compound is produced. After the reaction is completed, the obtained solution is filtered and dried at 80 to 150 ° C. for 10 to 15 hours to produce compound powders of the following chemical formulas 1 to 14.
[0025]
The positive electrode active material manufactured by the reflux method described in detail has a spherical shape or a similar spherical shape, a particle size of 10 nm to 10 μm, and a surface area of 0.1 to 5 m ² / g. Thus, the positive electrode active material of the present invention has a spherical shape or a similar spherical shape, so that the packing density can be increased during the production of the electrode plate. If the particle size of the positive electrode active material is smaller than 10 nm, there is a problem in battery safety (safety or thermal stability), and if it is larger than 10 μm, there is a problem in reactivity (kinetics). In addition, if the surface area of the positive electrode active material is smaller than 0.1 m ² / g, there is a problem in battery safety (safety or thermal stability), and if it is larger than 5 m ² / g, there is a problem in reactivity (kinetics). .
[0026]
Hereinafter, preferred examples and comparative examples of the present invention will be described. However, the following embodiment is only a preferred embodiment of the present invention, and the present invention is not limited to the following embodiment.
[0027]
(Example 1)
LiOH, Co (OH) ₂ and an aqueous KOH solution as starting materials were placed in a reflux flask volumetric flask, and then the temperature of the hot plate was increased to 180 ° C. At this temperature, the mixture was stirred for 24 hours to reflux. After the reaction was completed, the powder obtained by filtering the obtained solution was dried at 100 ° C. for 12 hours to synthesize the final LiCoO ₂ positive electrode active material powder.
[0028]
(Example 2)
The reaction was performed in the same manner as in Example 1 except that the reflux reaction was performed at 200 ° C.
[0029]
Example 3
The reaction was performed in the same manner as in Example 1 except that the reflux reaction was performed at 130 ° C.
[0030]
Example 4
The reaction was performed in the same manner as in Example 1 except that the reflux reaction was performed at 100 ° C.
[0031]
(Comparative Example 1)
LiCoO ₂ (Nippon Chem C-5 (average particle size is 5 μm)) powder was used as the positive electrode active material.
[0032]
The SEM (Scanning Electron-ic Microscopy) of Examples 1 and 2 and Comparative Example 1 are shown in FIGS. 2, 3 and 4, respectively. As shown in FIGS. 2 to 4, the active material produced by the methods of Examples 1 and 2 is contrary to the fact that a large number of fine particles having a size of 1 μm or less are collected to form particles having a size of about 1 μm. It can be seen that the active material of Comparative Example 1 is formed of single particles having an average of 5 μm. Moreover, it turns out that the shape of the active material of Examples 1 or 2 is a similar spherical shape closer to the spherical shape than the active material of Comparative Example 1.
[0033]
In addition, the XRD patterns of the active material manufactured by the methods of Examples 1 to 3 are shown in FIGS. 5B, 5A, and 5C, and the XRD pattern of the active material of Comparative Example 1 is shown in FIG. Indicated. As shown in FIG. 5, since the XRD pattern of the active material manufactured by the method of Examples 1 to 3 was similar to that of FIG. 6, it was manufactured by the method of Examples 1 to 3. It can be seen that the active material has a structure of LiCoO ₂ .
[0034]
At the same time, a lithium secondary battery was manufactured using the active material manufactured by the method of Example 2 and the active material of Comparative Example 1. The active material, the conductive agent, and the binder were mixed at a weight ratio of 94: 3: 3, and N-methylpyrrolidone was added to the mixture to prepare a positive electrode active material slurry. The positive electrode active material slurry was cast on an Al foil to produce a positive electrode, and a lithium secondary coin battery was produced using a lithium counter electrode. As the electrolytic solution, a mixture (1: 1 volume ratio) of ethylene carbonate and dimethyl carbonate in which 1M LiPF ₆ was dissolved was used.
[0035]
The charge / discharge characteristics and life characteristics of the batteries using the active materials of Example 2 and Comparative Example 1 manufactured were measured, and the results are shown in FIGS. The electrochemical characteristics were evaluated at a charge / discharge potential of 4.3V-2.75V. Life characteristics were 1 time at 0.1C, 3 times at 0.2C, 10 times at 0.5C, and finally 86 times at 1C. Was measured by continuously charging and discharging. As shown in FIG. 7, the charging characteristics are similar to those of the battery using the active material of Comparative Example 1, but it can be seen that the discharging characteristics are somewhat deteriorated. However, as shown in FIG. 8, the battery using the active material of Example 2 showed a capacity decrease of about 50 mAh / g after 86 cycles under 1C high rate charge / discharge conditions. It can be seen that the battery using the material showed a capacity reduction of 120 mAh / g. Therefore, it can be seen that the battery using the active material of Example 2 has better life characteristics than the battery using the active material of Comparative Example 1.
[0036]
【The invention's effect】
As described in detail, the positive electrode active material produced using the reflux method of the present invention has excellent charge / discharge life characteristics.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a reflux apparatus used in the present invention.
FIG. 2 is a SEM photograph of a positive electrode active material manufactured according to an embodiment of the present invention.
FIG. 3 is a SEM photograph of a positive electrode active material manufactured according to another example of the present invention.
FIG. 4 is an SEM photograph of a positive electrode active material of a comparative example.
FIG. 5 is a graph showing an XRD pattern of a positive electrode active material manufactured according to an embodiment of the present invention.
FIG. 6 is a graph showing an XRD pattern of a positive electrode active material of a comparative example.
FIG. 7 is a graph showing charge / discharge characteristics of a battery manufactured using a positive electrode active material according to an example of the present invention.
FIG. 8 is a graph showing life characteristics of batteries manufactured using positive electrode active materials of Examples and Comparative Examples of the present invention.
[Explanation of symbols]
1 container 3 hot plate 5 thermometer

Claims (6)

Characterized by producing a positive active material for a rechargeable lithium battery by refluxing the reaction of a lithium salt and a metal salt on a basic aqueous solution of KOH or NaOH, or KOH or on an organic solution of NaOH, lithium secondary batteries For producing a positive electrode active material for use. 2. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material is selected from compounds represented by chemical formulas 1 to 14 below.
[Chemical Formula 1] Li _x MnA ₂
[Chemical Formula 2] Li _x MnO _2-z A _z
[Chemical Formula 3] Li _x Mn _1-y M ′ _y A ₂
[Chemical Formula _{4] Li x Mn 1-y} M 'y O 2-z A z
[Chemical Formula 5] Li _x Mn ₂ O ₄
[Chemical Formula 6] Li _x Mn ₂ O _4-z A _z
[Chemical Formula 7] Li _x Mn _2-y M ′ _y A ₄
[Chemical Formula 8] Li _x BA ₂
[Chemical Formula 9] Li _x BO _2-z A _z
[Chemical Formula 10] Li _x B _1-y M ″ _y A ₂
[Chemical Formula 11] Li _x Ni _1-y Co _y A ₂
[Chemical Formula 12] Li _x Ni _1-y Co _y O _{2 -z} A _z
[Formula 13] Li _x Ni _1-yz Co _y M ″ _z A ₂
[Chemical Formula 14] Li _{x ′} Ni _{1-y ′} Mn _{y ′} M ′ _{z ′} A _α
(In the above formula, 0.95 ≦ x ≦ 1.1, 0.01 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.5, 0.95 ≦ x ′ ≦ 1, 0.01 ≦ y ′. ≦ 0.5, 0.01 ≦ z ′ ≦ 0.1, 0.01 ≦ α ≦ 0.5, and M ′ is made of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, and V. A transition metal selected from the group or at least one of lanthanoid metals, and M ″ is a transition metal selected from the group consisting of Al, Cr, Co, Mg, La, Ce, Sr, and V, or (One or more of the lanthanide metals, A is selected from the group consisting of O, F, S and P, and B is Ni or Co.) The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the reflux reaction is performed at a temperature of 100 to 500 ° C. for 12 to 96 hours. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the pH of the basic aqueous solution is 7 to 14. A compound selected from the following formulas 1 to 14 produced by the production method according to claim 1 , having a spherical or similar spherical shape, a particle size of 10 nm to less than 1 μm, 0.1 to A positive electrode active material for a lithium secondary battery having a surface area of 5 m ² / g.
[Chemical Formula 1] Li _x MnA ₂
[Chemical Formula 2] Li _x MnO _2-z A _z
[Chemical Formula 3] Li _x Mn _1-y M ′ _y A ₂
[Chemical Formula _{4] Li x Mn 1-y} M 'y O 2-z A z
[Chemical Formula 5] Li _x Mn ₂ O ₄
[Chemical Formula 6] Li _x Mn ₂ O _4-z A _z
[Chemical Formula 7] Li _x Mn _2-y M ′ _y A ₄
[Chemical Formula 8] Li _x BA ₂
[Chemical Formula 9] Li _x BO _2-z A _z
[Chemical Formula 10] Li _x B _1-y M ″ _y A ₂
[Chemical Formula 11] Li _x Ni _1-y Co _y A ₂
[Chemical Formula 12] Li _x Ni _1-y Co _y O _{2 -z} A _z
[Formula 13] Li _x Ni _1-yz Co _y M ″ _z A ₂
[Chemical Formula 14] Li _{x ′} Ni _{1-y ′} Mn _{y ′} M ′ _{z ′} A _α
(In the above formula, 0.95 ≦ x ≦ 1.1, 0.01 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.5, 0.95 ≦ x ′ ≦ 1, 0.01 ≦ y ′. ≦ 0.5, 0.01 ≦ z ′ ≦ 0.1, 0.01 ≦ α ≦ 0.5, and M ′ is made of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, and V. A transition metal selected from the group or at least one of lanthanoid metals, and M ″ is a transition metal selected from the group consisting of Al, Cr, Co, Mg, La, Ce, Sr, and V, or (One or more of the lanthanide metals, A is selected from the group consisting of O, F, S and P, and B is Ni or Co.) The positive active material are those prepared in step of refluxing the reaction of a lithium salt and a metal salt on a basic aqueous solution of KOH or NaOH, or on an organic solution of KOH or NaOH, lithium secondary according to claim 5 Positive electrode active material for batteries.

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